Pigmented prepress coatings for composition board

Abstract

Disclosed herein is a process for coating a fiber mat with a pigmented coating prior to subjecting the mat to heat and pressure treatment to form a composition board having a smooth, embossed or textured surface. The coating contains a mixture of an acrylic, hydroxyl or carboxyl functional vehicle, a melamine-based coating crosslinking agent for the vehicle, a high-melting wax, and a platelet form of talc. By employing this process, composition board products are obtained which have superior surfaces and surface finishes. In addition, these finishes inhibit composition board extractive migration which causes the formation of discolored spots on the finished composition board's surface.

What is claimed is: 
     
       1. In a process for manufacturing composition boards under heat and pressure comprising providing a composition board stock, coating the surface of the stock, hot pressing the coated stock at elevated temperatures and pressure into a solid composition board product, and releasing the composition board product from the press, the improvement of which comprises utilizing as a composition board coating composition, an acrylic emulsion present at about the 2.5 to 58 percent by weight solids level, in combination with a platelet talc present at about the 25 to 97 percent by weight solids level, a crosslinking agent for the acrylic emulsion present at about the 0.3 to 18 percent by weight solids level, and a high melting wax present at about the 0.2 to 12 percent by weight solids level. 
     
     
       2. The process of claim 1 wherein the acrylic emulsion is present at about the 76 percent by weight solids level, the platelet talc is present at about the 80 percent by weight solids level, the crosslinking agent is present at about the 1.7 percent by weight solids level, and the high melting wax is present at about the 2.5 percent by weight solids level. 
     
     
       3. The process of claim 1 wherein the platelet talc contains talc particles having aspect ratios in the range of about 10:1 to about 30:1. 
     
     
       4. The process of claim 1 wherein the wax is a carnauba-based wax. 
     
     
       5. The process of claim 1 wherein the crosslinking agent is a melamine-based crosslinking agent. 
     
     
       6. The process of claim the melamine-based crosslinking agent is a polymethoxymethylol melamine. 
     
     
       7. The process of claim 1 wherein the pH of the coating composition is in the range of about 8 to about 10. 
     
     
       8. The process of claim 1 wherein the acrylic emulsion contains styrene and methylmethacrylate. 
     
     
       9. The process of claim 1 wherein the coating composition contains flow control agents and fillers.